Opensourcing part of the application

how would you opensource part of the application in package based architecture?

I wanna keep packages which fetch external data from external APIs to myself.
But opensource the user facing part and all the other user interaction stuff.
So people can import demo DB dump and run all the stuff themselves.

And I want to have private and public git repos so I dont release something private to public by accident.

For now I am thinking about separate repos for every package.
And than have kinda umbrella packages, so user can add just umbrella package and it will require all the needed released parts on package level.
Only thing to get it working correctly would be to import DB dump, copy+change settings.json and meteor add myapp:released.

Any hints? :smiley: